The Elder Scrolls V: Skyrim was a massive hit, and as such it is somewhat surprising that it took Bethesda a full seven months to deliver the first proper DLC package for it, but on the other hand - Dawnguard delivers more punch than your average DLC add-on.
Dawnguard adds a brand new questline, split in two: do you choose to side with vampires or Dawnguard (a group of men dedicated to fighting the immortal bloodsuckers)? In terms of size it's around the same as a faction questline in Skyrim, perhaps even larger, but it also adds new ways of playing the game with players given the choice of becoming a vampire lord or a werewolf - both come with new perk trees and abilities.
Head back into Skyrim with add-on downloaded and guards and inn keepers will let you know that there is a group forming in an abandoned fort, calling themselves Dawnguard. Their mission in this world is to rid it off vampires - apparently a growing threat in Skyrim.
You need to be level ten for the questline to activate, and using my level 40 Nord warrior mage, made way to Fort Dawnguard outside of Riften (conveniently set in a hidden canyon somehow missed so far in previous treks through Skyrim).
You're introduced to the Dawnguard cause and their leader Isran, and you're given a crossbow (a new weapon type that will come in handy for those who climbed the archery skill tree) and a mission to find out what vampires are up to in a crypt in the Northern part of Skyrim. This is where you first face the night stalkers and you're introduced to why vampire activity is on the rise - soon after you will also be given a choice of whether to join their rank or stick with the Dawnguard.
As I'd already completed the Companion questline to gain beast form (werewolf), the choice was simple - stick with being a werewolf (enhanced with a perk tree and skills in Dawnguard) or become a Vampire Lord (with perk tree and skills).
I tried out both sides of the experience, and personally preference favoured the Vampire Lord. But both carry the same basic flaw - the player has to be in third person perspective. Sure you can lock the camera over the shoulder, but Elder Scrolls games are meant to be played in first person, and animations and locations just don't work well with the third person perspective.
This is especially true when you're levitating in Vampire Lord form using magic (there is also an option of straight melee fighting with your Vampire Lord on the ground). Even some of the questline specific locations had problems accomodating a levitating Vampire Lord without issues: let's not even get into trying the trick while inside a small cottage.
As a vampire your abilities may be a bit more interesting (I really enjoy the bat teleportation one), but ultimately as a level 40 I found that turning into a vampire or werewolf was making me significantly weaker in combat. As a vampire you can always use blood magic to get some health back, but until you climb the perk tree you're going to be fairly weak and as a vampire that requires you using your Vampire Lord form - while as a werewolf you need to feed off carcasses. Other than for novelty I rarely used these forms, and the transformation process also made it a bit of a chore paired with the fact that you can't manage items or pick up loot while in these forms.
One thing about being a vampire that I liked was how being out in the sun and being powerful was balanced. Basically if you feed on humans you're not damaged as much by sunlight (otherwise your regeneration of health, stamina and mana, is low or close to zero), but if you choose to do this you also weaken the potency of your vampire abilities. It's a nice balance in there, and those who don't care much about using their Vampire Lord form can feed on humans to cancel out the disadvantage of sunlight. As far as feeding goes there is also a useful skill that lets you passify a person so you can feed on them even when they're awake.
What was truly enjoyable with Dawnguard was the storyline. Well written like most of the faction/guild questlines in Skyrim, it offers a lot of added insights and some truly memorable characters. There are new dragon shouts to learn, the crossbow is a nice addition (especially if you stick with the Dawnguard as you'll be able to create crossbows and bolts yourself), the ability to recruit trolls as a Dawnguard is also a pretty cool feature. You can now also change your appearance in game, a nice little addition I'm sure some will toy around with from dusk 'til dawn.
There are new locations added with the expansion, and as with most of the other stuff found in Dawnguard it's a mixed bag. I enjoyed the dungeons, and the vampire castle off the coast of Solitude, but Soul Cairn was a bit of a disappointment.
I never really enjoyed the planes of Oblivion in The Elder Scrolls IV: Oblivion, and Blackreach with its crimson nirnroots also caused me a lot of frustration in Skyrim - and even if Soul Cairn isn't as bad as Blackreach, it's still an area that is difficult to navigate due to its design. It may look cool, but it took me almost an hour to get any bearing on the layout of the place and the local map is not very helpful in this regard. I'm also not a fan of the "collect 10 pages" or "harvest 25 husks" nature of the side quests in this area. From a story perspective, however it was enjoyable, so even if it was a bit frustrating it certainly had its moments.
With a beefy questline of around ten quests (some shorter, others longer), and with roughly the same amount of new side quests, plus lots of other new features - it's hard to fault the value of Dawnguard. It's definitely more sizeable than any of the expansions for Fallout 3, but with that said it adds maybe 5 per cent or so on top of what was already there in Skyrim, and as such the price tag of 1600 points becomes more of an issue.
Yet I suspect anyone who has been waiting for more Skyrim content will be reasonably pleased with what's in Dawnguard. It has issues with design (Soul Cairn), and there are quite a few bugs to contest (I was often faced with weapons of fallen foes being stuck mid-air), but ultimately it adds enough interesting story elements and lore to be worth the points.
Overall, I found Dawnguard to be a bit of a mixed bag. Compared to the content Skyrim offers it just didn't appeal to me as much, and the choice to make some of the key elements of the expansion locked in third person view is a mistake in my opinion. Soul Cairn, one of the key new areas of the expansion was also something of a let down, if not in terms of looks and storyline, then in terms of frustration level and meaningless collect quests.
On the other hand, the questline as such is very interesting, and it adds something to the overall Skyrim experience. We are introduced to more knowledge on Elder Scrolls and dragons as well as the intriguing concept of Soul Cairn. And given that I presume most players will want to explore both sides of the questline, there is definite value here even if 1600 points comes across as a little steep.